Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) device, especially a MEMS device capable of compensating a deformation of a mass structure and a MEMS compensation structure thereof.
Description of Related Art
Typically, a MEMS device is designed to sense a change of a capacitance generated by a movement of a mass structure therein. FIG. 1A shows a prior art MEMS device 10, wherein a mass structure 11 is connected to springs by anchors 101 located at peripheral sides of the mass structure 11, and the mass structure 11 forms a top capacitor circuit Ctop with a top electrode 12 and a bottom capacitor circuit Cbot with a bottom electrode 13 respectively. When the mass structure 11 moves relatively with respect to the top electrode 12 and the bottom electrode 13, the movement can be sensed according to the capacitance changes of the top capacitor circuit Ctop and the bottom capacitor circuit Cbot.
However, when the MEMS device 10 works under high temperature, the mass structure 11 may deform due to thermal expansion. Referring to FIG. 1B, as an example, the center of the mass structure 11 is deformed downward due to thermal expansion, which causes a decrease of the capacitance of the top capacitor circuit Ctop and an increase of the capacitance of the bottom capacitor circuit Cbot (as indicated by the directions of the arrows), and therefore the sensing result is inaccurate. The mass structure may deform not only because of thermal expansion but because of other reasons such as stress caused by a manufacturing step.
In view of the drawback of the prior art, the present invention provides a MEMS device having a compensation mass structure. The MEMS device includes a plurality of top electrodes, a plurality of bottom electrodes, and a mass structure having plural anchors. The projections of the plural top electrodes on the mass structure along a normal direction of the mass structure are located at opposite sides of each anchor, and the projections of the plural bottom electrodes on the mass structure along a normal direction of the mass structure are similarly located at opposite sides of each anchor, such that the deformation of the mass structure does not affect the sensing result. The present invention also provides a compensation mass structure corresponding to the MEMS device.